We have 12 pcs of 22gph nozzles and 6 EFI fuel pumps. The fuel pressure varies depending on the setting of the recirkulation valve, but goes from 30 psi and up.
According to the info I got, the engine should need about 12l/min to run.

There are no marks on our valves, so they have not been fully opened. On the other hand; the wont get fully opened if the engine is not running better. Or the engine will not run better if they don't open more. Think we got a "the hen and the egg" situation here .

Nozzles rated at 100psi , so at 30psi they'll be flowing ~55% of rated flow , so ~9 lpm , still a huge amount of fuel , but at 30psi the atomisation will be crap , and combined with your sub zero air temps , the combustion won't be all that good .

Maybe a suggestion or two ,

................remove the inlet diffuser ,

fit the airstart nozzles adjacent to the top row of spray nozzles ,

arrange your fuel manifold so that you can supply fuel to only the top/upper most spray nozzles near the air start injectors during initial startup , this will require higher pressure fueling to the limited number of nozzles for improved atomisation

if combustion appears to be OK , bring online another row of spray nozzles

I'd almost be inclined to hookup propane to one row of spray nozzles in the middle to provide a faster burning fuel to augment the liquid fuel spray from the top row .

You could also try blanking off some of your reed inlet area , I tried this with some success during the early development of my PJ , it produced a more reliable idle .

Rocket Man here I tried and tried to log in but can not get password to work so I gave up and made a new account with a new name. I have been doing research on pulse jet engines for 40 years. Your combustion chamber is too small all the fuel is trying to burn in the exhaust pipe. If you blow fuel down the engine in the direction of the exhaust pipe the fuel will type to burn in the tail pipe not the combustion chamber. Your valves appear to open too much. I have some test equipment that I built for my own testing each piece of the engine has to be tested to make sure it will work when combined with all the other pieces. I am sure I can make your engine run. You are building a 1/2 scale German WWII Argus engine I can get all the demensions I need from the German WWII full size drawings it will take me about 20 minutes to do the math. Read about Fuel Burn Rate in Liquid Fuel Rocket Engine design books. Fuel must have a large enough area to burn other wise it tries to burn in the exhaust system.

The German engine tail pipe diameter is 400 mm = 15.748 inches. I will do all my math in inches then convert it to metric. I hope I did not make any math errors online calculator will not do millimeters. Notice the exhaust pipe is 120" long that makes the engine start easy and run good it will throttle down to about 15% of full power. You can cut the exhaust pipe a couple feet shorter the engine will be harder to start and not throttle down as low and it will run hotter and cause more damage to the valves. Long exhaust pipe will be an advantage for your valves if they are opening too much. A=Cross sectional area. L=length. V=volume. D=diameter. R=radius.

From some rough calcs the airflow quantity required for this engine is nearly 3 times that of the previous kick engine. That appears to be a considerable amount.

I would recommend to apply the diffusor, but with a design that resembles more typical ejector intake designs.(this should help in reaching the x3 quantity when the compressed air is used with the eductor intake)

Intake/diffusor length does matter, and from what I can tell it needs to be in the neighborhood of 270mm in length.

A little extra flow from an industrial fan may provide a flow stream over the tail and increase the overall volume and velocity of flow through the engine.

It appears work is being done on leaning out the starting fuel flow.

Using thinner valve material appears to be an option as the current valves are reportedly a little "stiff".

PyroJoe wrote:From some rough calcs the airflow quantity required for this engine is nearly 3 times that of the previous kick engine. That appears to be a considerable amount.

I would recommend to apply the diffusor, but with a design that resembles more typical ejector intake designs.(this should help in reaching the x3 quantity when the compressed air is used with the eductor intake)

Intake/diffusor length does matter, and from what I can tell it needs to be in the neighborhood of 270mm in length.

A little extra flow from an industrial fan may provide a flow stream over the tail and increase the overall volume and velocity of flow through the engine.

It appears work is being done on leaning out the starting fuel flow.

Using thinner valve material appears to be an option as the current valves are reportedly a little "stiff".

Hope this helps

If the air intake cross sectional area is too large for the engine the engine will not suck the exhaust flame back into the compustion chamber to ignite the next supply of fuel. If the engine is too free flowing the exhaust just keeps going out the tail pipe nothing sucks back and the engine will not run. You can find out if air intake is too large just by blocking off some of the air intalk holes. Put a piece of sheet metal over part of your air intake then give it a test to see if it will start and run. But the engine still may not run if it has other problems. If the valve material is too thin and the valves open too easy it causes the same problem. If the valves open too far and are not matched to the pulse frequency of the engine the valves may still be open when the engine tries to suck the exhaust back it sucks in to much intake air this causes a very low vacuum and not much exhaust sucks back. Pulse jet engines appear to be simple but every part of the engine has to work with all the other parts. Rocket Man.

We have already planned to block some of the valves to make the intake area smaller.

Regarding the valves, I can't really see how they could be too thin. They are thicker than the valves of the original V1, and we have seen no proof at all for them opening fully and getting in contact with the diffusor. Personally, I believe we should try thinner valves. Maybe I am completely wrong, but at least I would earn some more experience

The length of the valves has been adapted to the (calculated) frequency of the engine. As soon as we get the engine running, we can measure the real frequency and maybe adjust the next set of valves.

Last edited by LinusN on Sun Apr 17, 2011 8:01 am, edited 1 time in total.

LinusN wrote:We have already planned to block some of the valves to make the intake area smaller.

Regarding the valves, I can't really see how they could be too thin. They are thicker than the valves of the original V1, and we have seen no proof at all for them opening fully and getting in contact with the diffusor. Personally, I believe we should try thinner valves. Maybe I am completely wrong, but at least I would earn some more experience

The length of the valves has been adapted to the (calculated) frequency of the engine. As soon as we get the engine running, we can measure the real frequency and maybe adjust the next set of valves.

Looking at the video it appears the fuel is not combusting inside the combustion chamber. The fuel seems to be blowing out the exhaust and trying to burn in the tail pipe and out the end. This tells me, combustion chamber is too small there is not enough room for the fuel to combust and build up pressure inside the engine. Fuel needs to combust and go BOOM slamming the valves shut and blowing all the burned exhaust out the tail pipe.

I did the math calculations on your engine. The tail pipe is too short it needs to be extended to a total length of 2860mm. The cone volume is 18.9% too small. Combustion chamber volume is 16% too small. Quick Fix add 18.9% + 16% = 34.9%. Increase the volume of your combustion chamber cut it in half then splice in 433mm so the total length of combustion chamber is 933mm. The engine should start fairly easy at 20% throttle.

I built myself a test guage to test how much force it takes to open a reed valve. I test the reed valves of a good running engine then I can do some math to determine how much force is needed to open reed valves on new engine I want to build that runs at a different frequency. I make a reed valve for the new engine then I use my tester to make sure it works correctly.

If you make the metal reed valve thicker the valves are harder to open and the valve frequency increases. If you make the metal thinner the valves open easier the frequency goes down. The thinner metal damages easier and valves tend to brake off and not last very long. Thin metal also tends to crack and the tip ends chip off. Valves that open too easy does not allow the engine to suck the exhaust back into the combustion chamber and reignite the next fuel/air mixture also too much cross sectional area on the air intake does the same thing.

Valve retainer needs to be designed so the reed valves do not hammer themself to death. Valves that open too much operate at a lower frequency than valves that open in a shorter distance. Correctly designed valves will extend their life several 100 times.

I still can NOT log on under my original user name Rocket Man. I do not remember my password and I am not sure which of my 3 email accounts I used. I could use some help getting logged in. Computers are not forgiving it pissed me off so I made a new user name UpYourHole.

I wouldn't think there would be trouble making pressure in a combustor that is overall near 380mm(14.96")in diameter by 900mm(35.43") in length, with a more conservative tail cross section ratio than the Argus.

It may be good to respect LinusN observation that thinner valves should be tested. At least before a cut and weld operation.

What I propose is at issue is the vapor rate of the fuel/flame speed could be slow, the valve system is not allowing enough air to flow, the start-up fuel rate is high or some combination of the three.

It nearly starts as is, but suppose this is what we would see if the valves were to thick.

Not sure why valves were chosen that are thicker than the V1. Maybe LinusN can explain? Maybe just a material availability option?

PyroJoe wrote:I wouldn't think there would be trouble making pressure in a combustor that is overall near 380mm(14.96")in diameter by 900mm(35.43") in length, with a more conservative tail cross section ratio than the Argus.

It may be good to respect LinusN observation that thinner valves should be tested. At least before a cut and weld operation.

What I propose is at issue is the vapor rate of the fuel/flame speed could be slow, the valve system is not allowing enough air to flow, the start-up fuel rate is high or some combination of the three.

It nearly starts as is, but suppose this is what we would see if the valves were to thick.

Not sure why valves were chosen that are thicker than the V1. Maybe LinusN can explain? Maybe just a material availability option?

You need to read about FUEL BURN RATE in any Liquid Fuel Rocket Engine design book then you will know why the combustion chamber needs to be a certain size. Most college and university libruaries will have one. If the fuel does not have enough room to burn in a combustion chamber then it blows out the exhaust pipe and tried to burn in the air. Fuel that is not burning inside the engine is NOT producing any engine thrust. Wasted fuel. Turn on your work shop torch and ignite the flame with NO oxygen the orange flame is about 6 to 8 inches long. Now turn on the oxygen the more oxygen the fuel gets the shorter the flame gets because the fuel is burning faster in a smaller space. Air is only about 30% oxygen the other 70% does not burn. Fuel/air mixture is about 15 parts air to 1 part fuel that means 70% of the air that the engine sucks in will not burn it just takes up space in the combustion chamber. When fuel burns its volume increases seveal times. You need enough room inside the combustion chamber for that to happen. It is very possible you have valve problems too. You need fix one problem at a time. Rocket Man, I wish I could remember my password.

Take a look at this video. Notice there is almost no flame coming out of the engine exhaust. All the fuel is being burned inside the engine. All the fuel is producing thrust. It runs most efficient like this and produces maximum thrust. No wasted fuel burning out in the open air.

I'll agree with Pyro on this one , gotta get that first big bang to get the system working , the original Argus used acetylene in cold weather , these guys are starting this engine in Arctic conditions , they need a "big bang" to get those valves opening , and to achieve that they'll need a fast burning fuel that'll burn over a wide A/F ratio , propane or acetylene will do that .......................gasoline in cold ambiant condition has lousy combustion speed , OK once the engine heats up .

Having made a number of turbine engines flametubes that can burn 2 litres of kero per minute in a length of of only a few inches , I can't see why this combustion chamber won't be big enough , it just needs the right combination of fuels and air .

I remember speeding a couple of days getting my turboprop PJ engine to fire up for the first time , but once I'd got it worked out it only took seconds after that.

This engine needs even more sophistication with the fuel and air presentation due to its large size to obtain a good "gut full" of combustable mix before the spark fires it off , then it'll need to maintain that nice even mix to continue combustion, in a large engine there are too many places for combustion not to take place and in consequence overall combustion and engine performance is degraded